Dual in-line packaging with improved moisture resistance

ABSTRACT

A dual in-line packaging comprises a substrate having a top surface, a bottom surface and a peripheral surface, semiconductor chips mounted on the top and bottom surfaces of the substrate, a plurality of terminals fixed to the substrate and projecting from the bottom surface of the substrate, a first layer made of a first material and covering the bottom surface of the substrate and the semiconductor chips, and a second layer made of a second material and covering the top surface of the substrate and the semiconductor chips. The first material is resilient and moisture resistant and the second material is hard compared to the first material.

This application is a continuation of application Ser. No. 474,957 filedFeb. 5, 1990, now abandoned.

BACKGROUND OF THE INVENTION

The present invention generally relates to dual in-line packagings andmethods of producing the same, and more particularly to a dual in-linepackaging with an improved moisture resistance and a method of producingthe same.

In order to provide a desired moisture resistance, an integrated circuitpackaging has a structure in which top and bottom surfaces of asubstrate are covered by a resin. However, there are demands for anintegrated circuit packaging with an improved moisture resistance suchthat the moisture resistance is maintained even when an external forceis applied on terminals of the integrated circuit packaging.

FIG.1 shows a conventional dual in-line packaging 1 of an integratedcircuit. The packaging 1 comprises a ceramic substrate 2, semiconductorchips 3 and 4 which are respectively mounted on top and bottom surfacesof the substrate 2, and terminals 5 and 6 which are fixed on both sidesof the substrate 2. A resin layer 7 is formed on the top portion of thepackaging 1 and a resin layer 8 is formed on the bottom portion of thepackaging 1. These resin layers 7 and 8 are made of a glass fiberreinforced phenolic resin. The packaging 1 is mounted on a printedcircuit board 9 by soldering the terminals 5 and 6 on the printedcircuit board 9.

The printed circuit board 9 may warp due to heat or the like. In thiscase, an external force is applied on the terminals 5 (or 6) due to thewarp. For example, the terminal 5 shown in FIG.2A may be pulled and bentas shown in FIG.2B by the external force. But when the terminal 5 isbent, cracks 10 may be formed in the resin layer 8 as shown in FIG.2Bbecause the glass fiber reinforced phenolic resin is a hard material.When the cracks 10 are formed in the resin layer 8, the moisture caneasily enter the inside of the packaging 1 and damage the integratedcircuits. As a result, the serviceable life of the packaging 1 isshortened by the deterioration of the moisture resistance caused by thecracks 10.

On the other hand, with regard to the top surface of the packaging 1, itis conceivable to thicken the resin layer 7 to reduce the irregularitieson the top surface and facilitate a printing on the top surface.However, when the thickness of the resin layer 7 is large, thecontraction stress is large when the phenolic resin hardens. As aresult, an active layer on the substrate 2 may separate from thesubstrate and the semiconductor chips 3 may float from the substrate 2.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful dual in-line packaging and a method of producing thesame wherein the problems described above are eliminated.

Another and more specific object of the present invention is to providea dual in-line packaging comprising a substrate having a top surface, abottom surface and a peripheral surface, semiconductor chips mounted onthe top and bottom surfaces of the substrate, a plurality of terminalsfixed to the substrate and projecting from the bottom surface of thesubstrate, the terminals being arranged in-line along parallel sides ofthe substrate, a first layer made of a first material and covering thebottom surface of the substrate and the semiconductor chips, and asecond layer made of a second material and covering the top surface ofthe substrate and the semiconductor chips, where the first material isresilient and moisture resistant and the second material is hardcompared to the first material. According to the dual in-line packagingof the present invention, it is possible to maintain the moistureresistance even when an external force is applied to the terminals andthe terminals are deformed.

Still another object of the present invention is to provide a method ofproducing a dual in-line packaging comprising the steps of preparing asubstrate having semiconductor chips mounted on top and bottom surfacesof the substrate and having plurality of terminals projecting from thebottom surface of the substrate, where the terminals are arrangedin-line along parallel sides of the substrate, forming a first layermade of a first material over the bottom surface of the substrate andthe semiconductor chips, and forming a second layer made of a secondmaterial over the top surface of the substrate and the semiconductorchips, where the first material is resilient and moisture resistant andthe second material is hard compared to the first material. According tothe method of the present invention, it is possible to improve themoisture resistance especially when a silicone resin is used for thefirst material and a phenolic resin containing fiber glass is used asthe second material.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG.1 is a cross sectional view showing an example of a conventionalintegrated circuit packaging;

FIGS.2A and 2B respectively are cross sectional views showing a portionof the conventional integrated circuit packaging shown in FIG.1 forexplaining the formation of cracks in the packaging;

FIG.3 is a cross sectional view showing an embodiment of a dual in-linepackaging according to the present invention;

FIG.4 is a perspective view showing a terminal portion of theembodiment;

FIGS.5A through 5C respectively are diagrams for explaining anembodiment of a method of producing the dual in-line packaging accordingto the present invention; and

FIGS.6A and 6B respectively are diagrams for explaining the embodimentwhen an external force is applied on terminals of the packaging.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG.3 shows an embodiment of a dual in-line packaging according to thepresent invention. In FIG.3, those parts which are substantially thesame as those corresponding parts in FIG.1 are designated by the samereference numerals, and a description thereof will be omitted.

Terminals 21 and 22 of a dual in-line packaging 20 respectively haveapproximately U-shaped portions 21a and 22a which engage respectivesides of the substrate 2 and approximately L-shaped portions 21b and 22bwhich connect to the respective U-shaped portions 21a and 22a and absorbthe stress. The terminals 21 are shown in FIG.4 on an enlarged scale.The U-shaped portion 21a of each terminal 21 fits over the side of thesubstrate 2 and is soldered on a land 23. The terminals 22 are solderedin a similar manner.

A silicone resin layer 25 covers a bottom surface 2a and a peripheralsurface 2c of the substrate 2. The silicone resin layer 25 has a rubberhardness of 80° or less. A glass fiber reinforced phenolic resin layer26 which is added with 80 vol % of fiber glass is formed on a topsurface 2a of the substrate 2 and a portion 25a of the silicone resinlayer 25 which covers the peripheral surface 2c of the substrate 25.

Next, a description will be given of an embodiment of a method ofproducing the dual in-line packaging according to the present invention,and particularly of the method of forming the resin layers 25 and 26.

In FIG.5A, the substrate 2 is positioned so that the bottom surface 2afaces up and a dispenser 27 is used to form the silicone resin layer 25.The silicone resin has a fine flow property and the silicone resinpositively enters to the rear side of the terminals 21 and 22. Hence, asshown in FIG.4, the silicone resin layer 25 completely covers theU-shaped portion 21a of each terminal 21 and forms a conical portion 25bin the periphery of the L-shaped portion 21b due to the surface tension.The silicone resin layer 25 also covers the peripheral surface 2c of thesubstrate 2.

Next, after the silicone resin layer 25 is hardened by a thermalprocess, the substrate 2 is dipped in a phenolic resin liquid 29 whichis added with 80 vol % of fiber glass so that both the top surface 2band the peripheral surface 2c of the substrate 2 are submerged in thephenolic resin liquid 29 as shown in FIG.5B.

Thereafter, the substrate 2 is pulled out of the phenolic resin layer 29as shown in FIG.5C. The phenolic resin which covers the substrate 2hardens by a thermal process to form the phenolic resin layer 26.

Hence, the silicone resin layer 25 covers the surfaces 2b and 2c of thesubstrate 2, and the phenolic resin layer 26 covers the surface 2a ofthe substrate 2 and a portion of the silicone resin layer 25.

Next, a description will be given of the moisture resistancecharacteristic of the dual in-line packaging 20 which is provided withthe resin layers 25 and 26.

The silicone resin layer 25 and the phenolic resin layer 26 themselvesrespectively have a high moisture resistance because both silicone resinand phenolic resin are moisture resistant materials.

Generally, the silicone resin has a poor adhesion with respect to otherresins. For this reason, a resin layer which is formed on a siliconeresin layer easily separates. But in the dip coating process describedabove in conjunction with FIG.5B, the phenolic resin liquid which isused is added with a large quantity of fiber glass and has a quick-drycharacteristic. For this reason, the adherence of the phenolic resinlayer 26 and the portion 25a of the silicone resin layer 25 issatisfactory, and the phenolic resin layer 26 does not easily separatefrom the silicone resin layer 25. Therefore, the moisture is positivelyprevented from entering the inside of the dual in-line packaging 20 viajunction interfaces 30 and 31 between the silicone resin layer 25 andthe phenolic resin layer 26.

FIGS.6A and 6B respectively are diagrams for explaining the embodimentwhen an external force is applied on the terminals 21 of the dualin-line packaging 20. When an external force is applied on the terminal21 in a direction A shown in FIG.6A due to a warping of the printedcircuit board 9 or the like, the L-shaped portion 21b of the terminal 21is bent and stretched as shown in FIG.6B to absorb the stress. Theexternal force which deforms the terminal 21 is also applied on thesilicone resin layer 25. However, the rubber hardness of the siliconeresin layer 25 is 80° or less, and the silicon resin layer 25 undergoesa resilient deformation depending on the deformation of the terminal 21.As a result, no cracks are formed in the silicone resin layer 25 evenwhen the terminal 21 is deformed by the external force. The siliconeresin layer 25 returns to its original state when the terminal 21returns to its original state free of the stress.

The terminal 22 and the silicone resin layer 25 undergo similardeformations when the external force is applied on the terminal 22.Hence, no cracks are formed in the silicone resin layer 25.

Accordingly, even when an external force is applied on the terminals 21and/or the terminals 22, the moisture resistance of the dual in-linepackaging is maintained to the initial moisture resistance.

Next, a description will be given of the characteristics of the phenolicresin layer 26 other than its moisture resistance characteristic. Thephenolic resin used in this embodiment is added with a large quantity offiber glass. For this reason, the contraction of the phenolic resinduring the thermal hardening is considerably small compared to the casewhere no glass fiber is added to the phenolic resin. Hence, the activelayer on the top surface 2b of the substrate 2 will not separate fromthe substrate 2 and the semiconductor chips 3 will not float from thesubstrate 2 when the thermal hardening of the phenolic resin layer 26takes place.

On the other hand, because the glass fiber reinforced phenolic resinlayer 26 is added with the large quantity of fiber glass, thecoefficient of thermal expansion of the glass fiber reinforced phenolicresin layer 26 is considerably small compared to the case where no fiberglass is added to the phenolic resin. Therefore, the coefficient ofthermal expansion of the phenolic resin layer 26 is similar to thecoefficient of thermal expansion of the ceramic substrate 2.Accordingly, a thermal stress not easily generated during the operationof the dual in-line packaging 20, and it is possible to prevent thesubstrate 2 from cracking and prevent cracks from being formed in thephenolic resin layer 26.

The phenolic resin layer 26 of this embodiment enables an ink printingto be made thereon because the phenolic resin layer 26 contains fiberglass. Further, the hardness of the phenolic resin layer 26 enables thephenolic resin layer 26 to sufficiently function as a protection layer.

Next, a description will be given of the characteristics of theterminals 21 and 22. The terminals 21 and 22 respectively have a stressabsorbing portion immediately below a connecting portion where theterminals 21 and 22 connect to the substrate 2. Thus, compared to thecase where the stress absorbing part is provided at an intermediate partof the terminal as in the case of the terminal 5 shown in FIG.1, it ispossible to mount the dual in-line packaging 20 on the printed circuitboard 9 with a height which is lower than that of the conventionalpackaging.

In the described embodiment, the layer 25 is 15 made of the siliconeresin and the layer 26 is made of the phenolic resin containing fiberglass. However, it is possible to use other materials for the layers 25and 26 as long as the layer 25 is made of a resilient material which hasa satisfactory moisture resistance and the layer 26 is made of arelatively hard material which also has a satisfactory moistureresistance. For example, the material used for the layer 25 may beselected from a group which includes polyurethane, polyurethane rubber,silicon rubber and flexible epoxy. On the other hand, the material usedfor the layer 26 may be selected from a group which includes melamineresin and epoxy resin containing fiber glass.

Moreover, the material used for the substrate 2 is not limited toceramics. For example, the substrate 2 may be made of an epoxy glass.

In addition, the shape of the terminals 21 and 22 is not limited tothose of the described embodiment. For example, the stress absorbingportion of the terminal may be located at an intermediate part of theterminal as in the case of the conventional packaging shown in FIG.1.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

What is claimed is:
 1. A dual in-line packaging comprising:a substratehaving a top surface, a bottom surface and a peripheral surface;semiconductor chips mounted on the top and bottom surfaces of saidsubstrate; a plurality of terminals fixed to said substrate andprojecting from the bottom surface of said substrate; a first layer madeof a first material and covering the bottom surface of said substrateand bottom surface mounted semiconductor chips, wherein a portion ofsaid first layer is in direct contact with the bottom surface of thesubstrate, and wherein said first layer has side portions having innersurfaces in direct contact with said substrate peripheral surface; and asecond layer made of a second material and covering the top surface ofsaid substrate and top surface mounted semiconductor chips, wherein aportion of said second layer is in direct contact with the top surfaceof the substrate, and wherein said second layer has side portions havinginner surfaces in direct contact with outer surfaces of said first layerside portions, said first material being resilient and moistureresistant, said second material being hard compared to said firstmaterial, said terminals being arranged in-line along parallel sides ofsaid substrate and penetrating through said first layer to therebymaintain the moisture resistance of said duel in-line packaging evenwhen an external force is applied to said terminals.
 2. The dual in-linepackaging as claimed in claim 1 wherein said terminals respectively havea stress absorbing portion for absorbing a stress which is generatedwhen the terminals are deformed by an external force.
 3. The dualin-line packaging as claimed in claim 2 wherein said terminalsrespectively have an approximately U-shaped portion which sandwiches aside portion of said substrate, and said stress absorbing portion has anapproximately L-shape which connects to said U-shaped portion.
 4. Thedual in-line packaging as claimed in claim 1 wherein said first materialis a silicone resin, and said second material is a phenolic resin whichcontains glass fiber.
 5. The dual in-line packaging as claimed in claim1 wherein said first material is selected from a group which includespolyurethane, polyurethane rubber, silicon rubber and flexible epoxy. 6.The dual in-line packaging as claimed in claim 1 wherein said secondmaterial is selected from a group which includes melamine resin andepoxy resin containing fiber glass.
 7. The dual in-line packaging asclaimed in claim 1 wherein said substrate is made of a material selectedfrom a group which includes ceramics and glass epoxy.
 8. The dualin-line packaging as claimed in claim 1 wherein said first layer furthercovers the peripheral surface of said substrate, and said second layerfurther covers a portion of said first layer covering the peripheralsurface of said substrate.
 9. A dual in-line packaging, comprising:asubstrate having a top surface, a bottom surface and a peripheralsurface; semiconductor chips mounted on the top and bottom surfaces ofsaid substrate; a plurality of terminals fixed to said substrate andprojecting from the bottom surface of said substrate; a first layer madeof a first material and covering the bottom surface of said substrateand bottom surface mounted semiconductor chips, wherein said first layerincludes side portions having inner surfaces in direct contact with saidperipheral surface of said substrate, wherein a portion of said firstlayer is in direct contact with the bottom surface of the substrate; anda second layer made of a second material and covering the top surface ofsaid substrate and top surface mounted semiconductor chips, wherein saidsecond layer includes side portions having inner surfaces in directcontact with outer surfaces of said first layer side portions, wherein aportion of said second layer is in direct contact with the top surfaceof the substrate, said first material being resilient and moistureresistant, said second material being hard compared to said firstmaterial, said terminals being arranged in-line along parallel sides ofsaid substrate and penetrating through said first layer to therebymaintain the moisture resistance of said dual in-line packaging evenwhen an external force is applied to said terminals.
 10. A dual in-linepackaging, comprising:a substrate having a top surface, a bottom surfaceand a peripheral surface; semiconductor chips mounted on the top andbottom surfaces of said substrate; a plurality of terminals fixed tosaid substrate and projecting from the bottom surface of said substrate;a first layer made of a first material and covering the bottom surfaceof said substrate and bottom surface mounted semiconductor chips,wherein said first layer includes side portions having inner surfaces indirect contact with said peripheral surface of said substrate, wherein aportion of said first layer is in direct contact with the bottom surfaceof the substrate; and a second layer made of a second material andcovering the top surface of said substrate and top surface mountedsemiconductor chips, wherein said second layer includes side portionshaving inner surfaces in direct contact with outer surfaces of saidfirst layer side portions, wherein a portion of said second layer is indirect contact with the top surface of the substrate, said firstmaterial being resilient and moisture resistant, said second materialbeing hard compared to said first material, said second layer having asubstantial quantity of fiber glass so as: (a) to provide an adherencebetween said side portions of said first and second layers to preventmoisture from entering therebetween, and (b) to have the coefficient ofthermal expansion of said second layer be similar to that of saidsubstrate to thereby prevent the generation of thermal stress and cracksin said second layer, said terminals being arranged in-line alongparallel sides of said substrate and penetrating through said firstlayer to thereby maintain the moisture resistance of said dual in-linepackaging even when an external force is applied to said terminals.